Hi guys!

First of all, sorry for my poor english and short translation:)

Now everyone could access rating formulas, and there is some not obvious mathematic formulas. So, I decided to check probability formula(probability that the i-th participant has better result than the j-th participant). There was a lot of rating codeforces rounds, so it's easy to calculate this value by existing results. I choose cf rounds №200 — №350 (separately for each division). To solve this problem I wrote java program (sources). After getting results I copy/paste it to Excel and get plots:

for first division

for second division

Looks good, but lets try found something better:)

Unfortunately this formula doesn't look scientific, so I a little bit change it:

Now, lets build plots again

for first division

for second division

Now it's closer:)